University of Wisconsin-Madison student Marisa Weich contends with sub-zero wind chill temperatures while making her way to class on the campus Tuesday. / John Hart, AP

by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

Ferocious cold continued its assault on the north-central and northeastern USA on Wednesday. Wind chill temperatures dropped to -50 degrees in some parts of the upper Midwest.

Authorities suspect exposure has played a role in at least four deaths so far.

The 15 degree reading Wednesday morning in Washington, D.C., was the coldest temperature there in almost four years. The lows of 11 in New York City and 12 in Philadelphia were those city's coldest readings in nearly two years.

International Falls, Minn., the so-called "IceBox of the Nation," dropped to -20 degrees Wednesday morning. The city could approach an all-time record low temperature Thursday morning, according to Weather Channel meteorologist Jonathan Erdman. The forecast temperature early Thursday is -49 degrees; the all-time record low is -55 degrees.

"I am wearing a Snuggie under a top and another jacket over that," Faye Whitbeck, president of the chamber of commerce in International Falls, said on Tuesday. The city has remained below zero since Saturday morning.

In nearby Duluth, the city was below zero for 82 consecutive hours this week. That streak ended Wednesday morning, with a warm-up to 4 degrees.

The Northeast was also frigid: The wind chill Wednesday morning on the top of Mount Washington, N.H., was -85 degrees as the winds howled to 69 mph. Estcourt Station, Maine, was -36 degrees.

A ski resort in New Hampshire shut down on Wednesday and will remain closed Thursday because of unsafe ski conditions: a predicted wind chill of -48 degrees.

In Ocean City, Md., the seaside resort is having its boardwalk rebuilt in time for the spring. "It's not too bad," said Jake Stoltzfus, a subcontractor on the project from Lancaster County, Pa. "Your feet are the worst part. You gotta just dress warm. It takes some getting used to.

"This cold is no big deal, but the wind, that'll cut right through you," he added. "I'd say it's at least 5 degrees, with the wind chill."

Daytime highs on Wednesday remained below zero for parts of the Upper Midwest and in the teens across much of the Great Lakes, Ohio Valley and Northeast, the National Weather Service reported. Wind chill advisories are in effect from the Dakotas to Maine and as far south as Virginia.

The bitter conditions are expected to persist into the weekend in the Midwest through the eastern half of the U.S., said Shawn DeVinny, a National Weather Service meteorologist in suburban Minneapolis.

In an online bulletin, the weather service reported that "over the next few days, sub-freezing high temperatures are likely to continue north of the Ohio River and north of Virginia. This is the result of a strong cold front that moved through the region on Monday."

It won't be until early next week that milder air works its way into the central and eastern U.S., returning temperatures closer to normal, says AccuWeather meteorologist Tom Kines.

Police in Milwaukee, where the temperature was just 2 degrees at noon Tuesday, checked under freeway overpasses to find the homeless and urge them to find a shelter. The United Way of Greater Milwaukee has donated $50,000 to two homeless shelters so they can open overflow centers.

"We're incredibly relieved," said Donna Rongholt-Migan, executive director of the Cathedral Center, a Milwaukee shelter that received $25,000. "I was walking my dog last night and I couldn't feel my legs just after walking around the block."

Schools across the region either started late or didn't open at all. Districts in Duluth, Minn., and Ashland, Bayfield, Hurley, Washburn and Superior in far northern Wisconsin closed amid warnings that the wicked wind chills could freeze exposed flesh within a minute.

"It's brutal," Courtney Thrall, a 21-year-old University of Wisconsin-Madison student, said as she waited for her bus, her fur-trimmed parka hood pulled over her head.

Lake-effect snow has also been piling up near the Great Lakes: Bennetts Bridge, N.Y., has picked up more than 2 and a half feet of snow in the past two days, according to Weather Underground meteorologist Jeff Masters.

More lake-effect snow is likely Thursday, the weather service reports: "A variety of winter weather advisories and warnings are in effect for much of Michigan and also downwind of Lakes Erie and Ontario."

A pair of small winter storms -- one Wednesday night and another Friday -- are forecast to affect portions of the Ohio Valley and Mid-Atlantic, Kines says. Wednesday night's storm could bring an inch or less, while the next storm could bring "a large area of 1-3 inches from the Lower Lakes to the Ohio Valley to the Mid-Atlantic," he says.

The Friday storm won't be crippling, but even a light snowfall can be a big deal to people in Tennessee or North Carolina, Kines says. Washington, Baltimore, and Philadelphia are expected to see from 1-3 inches on Friday.

While the north freezes, record high temperatures were set this week in the West. Wednesday, a record high of 67 degrees was recorded in Colorado Springs. On Tuesday, there were record highs of 81 in Phoenix and Tucson and 80 in San Diego.